A known electronic engine control system comprises a processor-based engine controller that processes data from various sources to develop control data for controlling certain functions of the engine, including fueling of the engine by injection of fuel into engine combustion chambers. Control of engine fueling involves several factors. One is the quantity of fuel injected during an injection. Another is the timing of an injection. Consequently, the control system must set both the quantity of fuel injected and the time at which the injection occurs during an engine operating cycle.
A known diesel engine that powers a motor vehicle has an oil pump that delivers oil under pressure to an oil rail serving electric-actuated fuel injectors that use oil from the oil rail to force injections of fuel. Fuel under pressure is supplied to the fuel injectors via a fuel rail.
The pressure in the oil rail is sometimes referred to as injection control pressure, or ICP, and that pressure is under the control of an appropriate ICP control strategy that is an element of the overall engine control strategy implemented in the engine control system. ICP is a factor in controlling the quantity of fuel injected during an injection.
Examples of fuel systems containing fuel injectors that utilize ICP oil to force fuel into engine combustion chambers via plungers are found in U.S. Pat. Nos. 5,460,329; 5,597,118; 5,722,373; and 6,029,628.
A representative HEUI fuel injector has a plunger that is displaced within an internal pumping chamber by oil at ICP from an oil rail when a normally closed control valve in the injector opens in response to a signal from the engine controller to inject fuel into a combustion chamber. The oil acts via the plunger to amplify the fuel pressure in the pumping chamber to a magnitude large enough to force a normally closed valve at an outlet of the fuel injector to open. When the latter valve opens, the amplified fuel pressure forces fuel through the outlet and into the combustion chamber.
The injection is terminated by terminating the signal that caused the control valve to open. When that happens, the valve at the fuel injector outlet returns to normally closed condition, and fuel flows from the fuel rail to refill the pumping chamber, forcing the plunger to retract in the process.
Because ICP in the oil rail is a significant factor in controlling the quantity of fuel injected during an injection, the ability to accurately control ICP is of obvious importance in an engine control strategy. Control of ICP is typically somewhat complicated because changing engine conditions can act in ways that tend to change ICP. Various strategies exist for controlling ICP, such as the one described in U.S. Pat. No. 6,850,832.
When a fuel-injected diesel engine is being operated at high speed and high load, the fuel injectors operate near or at the limit of their capability where the frequency of operation and the quantity of fuel injected per injection are near or at their maximums. Consequently, full recharging of a fuel injector after the termination of an injection requires that a maximum, or near maximum, quantity of fuel flow into the pumping chamber within a minimum, or near minimum, amount of time.